Polyacetal resins are well-balanced among mechanical strength, chemical resistance, and excellent frictional wear properties and at the same time, they can be processed easily. As typical engineering plastics, polyacetal resins are used over a wide range of applications mainly for electrical appliances, mechanism parts for electrical appliances, automotive parts, and other mechanism parts. With expansion of application fields, however, polyacetal resins are required to reduce generation of formaldehyde, have dimensional stability after aging, have hot water resistance, reduce an amount of mold deposit, reduce an amount of formaldehyde generated after sliding, and suppress crack generation under aging. Thus, there is an increasing demand for polyacetal resins having various properties at a higher level.
With a view to satisfying such requirements, particularly with a view to satisfying the requirement for reducing generation of formaldehyde, there are investigated a process of adding guanamine and a hydrazide compound to a polyacetal resin composition (refer to, for example, Patent Documents 1 and 5), a process of adding a carboxylic acid hydrazide compound (refer to, for example, Patent Documents 2, 3, and 4), a process of adding a hydrazide compound (refer to, for example, Patent Document 6 and 7), and a method of adding an aromatic dihydrazide compound and an aliphatic hydrazide compound (refer to, for example, Patent Document 8).
[Patent Document 1] Japanese Patent Application Laid-open No. 2008-7676
[Patent Document 2] Japanese Patent Application Laid-open No. 4-345648
[Patent Document 3] Japanese Patent Application Laid-open No. 10-298401
[Patent Document 4] Japanese Patent Application Laid-open No. 2007-91973
[Patent Document 5] Japanese Patent Application Laid-open No. 2007-51205
[Patent Document 6] Japanese Patent Application Laid-open No. 2006-306944
[Patent Document 7] Japanese Patent Application Laid-open No. 2006-45489
[Patent Document 8] Japanese Patent Application Laid-open No. 2005-325225